WO2015164314A1

WO2015164314A1 - Subsea accumulator

Info

Publication number: WO2015164314A1
Application number: PCT/US2015/026788
Authority: WO
Inventors: Charles Edward Higham Tyrrell
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2014-04-23
Filing date: 2015-04-21
Publication date: 2015-10-29

Abstract

A subsea accumulator comprising: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein a first chamber is defined by the bottom surface, the outer wall, and the first piston; a second chamber is defined by the outer wall, the interior wall, and the first piston; a third chamber is defined by the interior wall, the outer wall, and the second piston; a fourth chamber is defined by the outer wall, the top surface, and the second piston.

Description

SUBSEA ACCUMULATOR

BACKGROUND

[0001] This application claims the benefit of U.S. Provisional Application No. 61/983,261, filed April 23, 2014, the entirety of which is incorporated herein by reference.

BACKGROUND

[0002] The present disclosure relates generally to subsea accumulators. More specifically, in certain embodiments the present disclosure relates to subsea accumulators useful for actuating blowout preventers and associated methods.

[0003] Considerable safety measures are required when drilling for oil and gas on- shore and off-shore. One such safety measure is the use of blowout preventers (BOPs). BOPs are basically large valves that close, isolate, and seal the wellbore to prevent the discharge of pressurized oil and gas from the well during a kick or other event. One type of BOP used extensively is a ram-type BOP. This type of BOP uses two opposing rams that close by moving together to either close around the pipe or to cut through the pipe and seal the wellbore.

[0004] The blowout preventers are typically operated using pressurized hydraulic fluid to control the position of the rams. Most BOPs are coupled to an accumulator or another source of pressurized hydraulic fluid. In most applications, multiple BOPs are combined to form a BOP stack, and this may include the use of multiple types of BOPs. In some applications, several hundred gallons of pressurized hydraulic fluid may have to be stored in accumulators at the BOP to be able to operate the BOP.

[0005] BOPs may be actuated by an accumulator. Traditional accumulators use a gas as a 'spring' to provide fluid storage at pressure. When these devices are taken subsea, the gas spring may need to be pre-charged to high pressures. This may result in very low efficiencies as the gas becomes less compressible at greater depths. A typical deepwater gas accumulator may provide only ½ gallon of "useable" fluid from an 11+ gallon accumulator. At extreme depths even greater challenges emerge as the gas becomes effectively incompressible and no longer acts as a good spring. This may require deepwater BOPs to carry more and more accumulators to achieve the necessary stored volume, creating very significant size and weight issues. A modern, deepwater BOP stack can require more than 100 accumulators in order to provide sufficient useable fluid volume.

[0006] It is desirable to develop an actuator for blowout preventers that do not require large number of bottles of accumulators. SUMMARY

[0007] The present disclosure relates generally to subsea accumulators. More specifically, in certain embodiments the present disclosure relates to subsea accumulators useful for actuating blowout preventers and associated methods.

[0008] In one embodiment, the present disclosure provides a subsea accumulator comprising: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein a first chamber is defined by the bottom surface, the outer wall, and the first piston; a second chamber is defined by the outer wall, the interior wall, and the first piston; a third chamber is defined by the interior wall, the outer wall, and the second piston; a fourth chamber is defined by the outer wall, the top surface, and the second piston.

[0009] In another embodiment, the present disclosure provides a blowout preventer system comprising: a blowout preventer and subsea accumulator, wherein the subsea accumulator comprises: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein a first chamber is defined by the bottom surface, the outer wall, and the first piston; a second chamber is defined by the outer wall, the interior wall, and the first piston; a third chamber is defined by the interior wall, the outer wall, and the second piston; a fourth chamber is defined by the outer wall, the top surface, and the second piston.

[0010] In another embodiment, the present disclosure provides a method of actuating a blowout preventer comprising: providing a blow out preventer providing a subsea accumulator, wherein the subsea accumulator comprises: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein a first chamber is defined by the bottom surface, the outer wall, and the first piston; a second chamber is defined by the outer wall, the interior wall, and the first piston; a third chamber is defined by the interior wall, the outer wall, and the second piston; a fourth chamber is defined by the outer wall, the top surface, and the second piston; connecting the subsea accumulator to the blowout preventer via a work line, wherein the work line comprises an actuating valve; and opening the actuating valve to actuate the blowout preventer. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.

[0012] Figure 1 illustrates a subsea accumulator in accordance to certain embodiments of the present disclosure.

[0013] Figure 2 illustrates a subsea blowout preventer system in accordance to certain embodiments of the present disclosure.

[0014] The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the disclosure.

DETAILED DESCRIPTION

[0015] The description that follows includes exemplary apparatuses, methods, techniques, and/or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.

[0016] The present disclosure relates generally to subsea accumulators. More specifically, in certain embodiments the present disclosure relates to subsea accumulators useful for actuating blowout preventers and associated methods.

[0017] One potential advantage of the subsea accumulators discussed herein is that they may utilize the ambient seawater pressure at depth as an advantage of the system, thus providing a very large useable fluid volume relative to the overall size of the accumulator. With this system, one or two accumulators may be sufficient to operate the entire subsea blowout preventer system. Another potential advantage is that because one piston may be open to the subsea environment, it may be very simple to mount a position sensor on the piston to determine piston position and hence volume. Another potential advantage is that the hydraulic pressure provided throughout the stroke of the accumulator is nearly constant, providing full shear force throughout the BOP shear ram stroke.

[0018] Referring now to Figure 1, Figure 1 illustrates subsea accumulator 100 in accordance with certain embodiments of the present disclosure. In certain embodiments, subsea accumulator 100 may be cylindrically shaped. Subsea accumulator 100 may comprise outer wall 101, top surface 102, bottom surface 103, interior wall 104, and piston system 180. In certain embodiments, piston system 180 may comprise a first piston 151, a second piston 152, and a connecting rod 150. In certain embodiments, subsea accumulator 100 may have a diameter in the range of from 2 to 24 inches. In certain embodiments, subsea accumulator 100 may have a diameter in the range of from 10 to 12 inches. In certain embodiments, subsea accumulator 100 may have a length in the range of from 1 to 20 feet. In certain embodiments, subsea accumulator 100 may have a length in the range of from 5 to 10 feet. In certain embodiments, subsea accumulator 100 may be constructed out of any material suitable for use as a subsea accumulator. In certain embodiments, subsea accumulator 100 may be constructed out of corrosion-resistant alloys such as stainless steel.

[0019] Subsea accumulator 100 may comprise several internal chambers defined in part by piston system 180. In certain embodiments, subsea accumulator 100 may comprise first chamber 110, second chamber 120, third chamber 130, and fourth chamber 140.

[0020] In certain embodiments, first chamber 110 may be a vacuum chamber. In certain embodiments, first chamber 110 is sealed from the outside environment. In certain embodiments, first chamber 110 may be completely void or contain a gas at a pressure significantly lower than ambient pressure subsea. In certain embodiments, first chamber 110 may contain a gas at a pressure in the range of from 0 to 15 psia. In certain embodiments, first chamber 110 may contain a gas at a pressure in the range of from 0 to 30 psia. In certain embodiments, first chamber 110 may contain a gas at a pressure in the range of from 0 to 5 psia. In certain embodiments, first chamber 110 may contain a gas at a pressure in the range of from 0 to 1 psia. In certain embodiments, first chamber 110 may have a diameter in the range of from 2 to 24 inches. In certain embodiments, first chamber 110 may have a diameter in the range of from 10 to 12 inches. In certain embodiments, first chamber 110 may be defined as the internal volume of subsea accumulator 100 below first piston 151. In certain embodiments, one or more seals 153 on first piston 151 may provide a seal between first chamber 110 and second chamber 120.

[0021] In certain embodiments, second chamber 120 may be a sea water flooded chamber. In certain embodiments, second chamber 120 may be open to the outside environment via inlet 105. In certain embodiments, inlet 105 may permit sea water or other fluids/gasses to flow in and out of second chamber 120. In certain embodiments, inlet 105 may be 1" in diameter.

[0022] In certain embodiments, second chamber 120 may be flooded with sea water and have a pressure equal to the pressure of the ambient sea water. In certain embodiments, the pressure within second chamber 120 may be in the range of from 15 to 5,000 psia. In certain embodiments, second chamber 120 may have a diameter in the range of from 2 to 24 inches. In certain embodiments, second chamber 120 may have a diameter in the range of from 10 to 12 inches. In certain embodiments, second chamber 120 may have a length in the range of from 1 to 10 inches. In certain embodiments, second chamber 120 may have a length in the range of from 2 to 5 inches. In certain embodiments, second chamber 120 may be defined as the internal volume of subsea accumulator 100 above first piston 151 and below interior wall 104. In certain embodiments, one or more seals 153 may provide a seal between first chamber 110 and second chamber 120. In certain embodiments, one or more seals 155 may provide a seal between second chamber 120 and third chamber 130.

[0023] In certain embodiments, third chamber 130 may be a hydraulic chamber. In certain embodiments, third chamber 130 may be in fluid communication with inlet 106. In certain embodiments, inlet 106 may permit hydraulic fluid to flow in and out of third chamber 130. In certain embodiments, inlet 106 may be 1" in diameter.

[0024] In certain embodiments, third chamber 130 may be filled with hydraulic fluid and have pressure greater than the pressure of the sea water. In certain embodiments, the pressure within third chamber 130 may be in the range of from 15 to 20,000 psia. In certain embodiments, the pressure within third chamber 130 may be twice that of the pressure within second chamber 120 and/or twice that of the pressure within fourth chamber 140. In certain embodiments, the pressure within third chamber 130 may greater than twice the pressure within second chamber 120 and/or greater than twice the pressure within fourth chamber 140. In certain embodiments, for example when the pressure within second chamber 120 and/or fourth chamber 140 is over 1000 psia, the pressure within third chamber 130 may from 0.1 to 5% greater than twice the pressure within second chamber 120 and/or fourth chamber 140. In certain embodiments, third chamber 130 may have a diameter in the range of from 2 to 24 inches. In certain embodiments, third chamber 130 may have a diameter in the range of from 10 to 12 inches. In certain embodiments, third chamber 130 may have a length in the range of from 1 to 10 inches. In certain embodiments, third chamber 130 may have a length in the range of from 2 to 5 inches. In certain embodiments, third chamber 130 may be defined as the internal volume of the subsea accumulator 100 above second piston 152 and above interior wall 104. In certain embodiments, one or more seals 153 may provide a seal between third chamber 130 and fourth chamber 140. In certain embodiments, one or more seals 155 may provide a seal between second chamber 120 and third chamber 130.

[0025] In certain embodiments, fourth chamber 140 may be a sea water flooded chamber. In certain embodiments, fourth chamber 140 may be open to the outside environment via inlet 107. In certain embodiments, inlet 107 may permit sea water or other fluids/gasses to flow in and out of fourth chamber 140. In certain embodiments, inlet 107 may be 1" in diameter.

[0026] In certain embodiments, fourth chamber 140 may be filled with sea water and have a pressure equal to the ambient pressure of the sea water. In certain embodiments, the pressure within fourth chamber 140 may be in the range of from 15 to 5,000 psia. In certain embodiments, fourth chamber 140 may have a diameter in the range of from 2 to 24 inches. In certain embodiments, fourth chamber 140 may have a diameter in the range of from 10 to 12 inches. In certain embodiments, fourth chamber 140 may have a length in the range of from 1 to 10 inches. In certain embodiments, fourth chamber 140 may have a length in the range of from 2 to 5 inches. In certain embodiments, fourth chamber 140 may be defined as the internal volume of the subsea accumulator 100 above second piston 152. In certain embodiments, one or more seals 153 may provide a seal between third chamber 130 and fourth chamber 140.

[0027] In certain embodiments, piston system 180 may comprise a first piston 151, a second piston 152, a connecting rod 150, and one or more seals 153 and 155. First piston 151, second piston 152, and connecting rod 150 may each be constructed out of any suitable material. In certain embodiments, first piston 151, second piston 152, and connecting rod 150 may each be constructed out of corrosion-resistant alloys such as stainless steel. In certain embodiments, connecting rod 150 may have a diameter in the range of from 2 to 12 inches. In certain embodiments, connecting rod 150 may have a diameter in the range of from 4 to 6 inches.

[0028] In certain embodiments, piston system 180 may capable of moving up and down within subsea accumulator 100 depending on the pressure and volume changes within first chamber 110, second chamber 120, third chamber 130, and fourth chamber 140 of subsea accumulator 100. For example, when the pressure in second chamber 120 and fourth chamber 140 are increased to at least half of the pressure in third chamber 130 (for example when subsea accumulator is being lowered into a subsea environment), piston system 180 may move downward compressing the hydraulic fluid in third chamber 130 to a pressure twice that of third chamber 120 and fourth chamber 140. Conversely, when the pressure in second chamber 120 and fourth chamber 140 are decreased to less than half of the pressure in third chamber 130 (for example when being used to actuate a blowout preventer), piston system 180 may move upward decompressing the hydraulic fluid in third chamber 130 to a pressure of half that of second chamber 120 or fourth chamber 140.

[0029] Similarly, in certain embodiments, when hydraulic fluid is added to third chamber 130, piston system 180 may move upward until the pressure in third chamber 130 is equal to twice the pressure in second chamber 120 or fourth chamber 140 (i.e. ambient pressure). Conversely, in certain embodiments, when hydraulic fluid is removed from third chamber 130, piston system 180 may move downward until the pressure in third chamber 130 is equal to twice the pressure in second chamber 120 or fourth chamber 140 (i.e. ambient pressure).

[0030] In certain embodiments, subsea accumulator 100 may further comprise fill line 108 and work line 109. Fill line 108 and work line 109 may both be connected to inlet 106. Fill line 108 may include fill valve 111 and may be used to transfer hydraulic fluid into third chamber 130 from a hydraulic fluid source. In certain embodiments, fill valve 111 may be a non-return valve. In certain embodiments, fill line 108 may include a relief valve 113. Work line 109 may include work valve 112 and may be used to provide hydraulic pressure from third chamber 130 to an actuator of a blowout preventer. In certain embodiments, work valve 112 may be a pilot operated control valve.

[0031] In certain embodiments, fill line 108 and work line 109 may be the same line or converge into a single line 114. In certain embodiments not illustrated, inlet 106 may comprise a first inlet 106 connected to fill line 108 and a second inlet 106 connected to work line 109. In certain embodiments, work line 109 may be connected to a ram of a blowout preventer. In certain embodiments, fill line 108 may be connected to a hydraulic fluid source.

[0032] In certain embodiments, subsea accumulator 100 may further comprise piston position sensor 160. In certain embodiments, piston position sensor 160 may be a linear position sensor to measure piston location to infer stored hydraulic fluid volume in chamber 130. In certain embodiments, piston position sensor 160 may be disposed within second chamber 120 or fourth chamber 140. As second chamber 120 and fourth chamber 140 may be open to ambient conditions, piston position sensor 160 may be able to determine the position of piston system 180 (and thus allow calculations of the volumes of first chamber 110, second chamber 120, third chamber 130, and fourth chamber 140) without creating a potential leak path into chambers 110 and 130.

[0033] Alternatively, or in addition to, subsea accumulator 100 may further comprise one or more pressure regulators 170. Pressure regulators 170 may be placed in inlet 105 and/or inlet 107. Examples of suitable pressure regulators may be hydraulic fluid pressure regulators. In certain embodiments, use of one or more pressure regulators 170 allows for the control of the pressure within first chamber 110, second chamber 120 and hence adjust the pressure in third chamber 130.

[0034] Referring now to Figure 2, Figure 2 illustrates a blowout preventer system 200 in accordance with certain embodiments of the present disclosure. As can be seen in Figure 2, blowout preventer system 200 may comprise one or more subsea accumulators 210, blowout preventer 220, well 230, well head 240, hydraulic fluid source 250, one or more work lines 260 comprising an actuator valve 261 and a relief valve 262, and one more fill lines 270 comprising fill valve 271 and a relief valve 272. Subsea accumulator 210 may have the same features discussed above with respect of subsea accumulator 100.

[0035] In certain embodiments, blowout preventer 220 may comprise a single blowout preventer or multiple blowout preventers arranged in a stack. In certain embodiments, blowout preventer 220 may comprise any conventional blowout preventer. In certain embodiments, blowout preventer 220 may be attached to a wellhead 240 on top of well 230.

[0036] In certain embodiments, blowout preventer 220 may be connected to one or more subsea accumulators 210 through one or more work lines 260. In other embodiments, one or more work lines 260 may be connected to the hydraulic chamber of subsea accumulator 210 and the rams of blowout preventer 220. In such embodiments, hydraulic pressure would actuate blowout preventer 220 when actuator valve 261 is opened.

[0037] In certain embodiments, the present disclosure provides a method of actuating a blowout preventer comprising: providing a blowout preventer; providing a subsea accumulator; connecting the subsea accumulator to the blowout preventer via a work line, wherein the work line comprises an actuating valve; and opening the actuating valve.

[0038] In certain embodiments, the subsea accumulator may be provided by lowering the subsea accumulator into the subsea environment. In some embodiments, the subsea accumulator may be pre-charged by pressurizing the hydraulic fluid in the third chamber before lowering the subsea accumulator into the subsea environment. In other embodiments, the hydraulic fluid in the third chamber may be at atmospheric pressure before it is lowered into the subsea environment. Regardless, as the subsea accumulator is lowered into the subsea environment, pressure from the ambient sea water will apply force to the first and second pistons further compressing the hydraulic fluid in the third chamber.

[0039] Once lowered into the subsea environment, the subsea accumulator may be connected to the blowout preventer via a work line. In certain embodiments, the work line is connected to the hydraulic chamber of the subsea accumulator and the rams of the blowout preventer. In instances where the work line is connected to the hydraulic chamber of the subsea accumulator and the rams of the blowout preventer, pressure from the hydraulic fluid will actuate the rams when the actuator valve is opened.

[0040] After the blowout preventer has been actuated, the subsea accumulator may be recharged by closing the actuator valve on the work line and opening the fill valve on the fill line, thus re -pressurizing the hydraulic fluid in the hydraulic chamber. In certain embodiments, once the actuator valves are closed on the work lines, the relief valves may be opened so that the rams of the blow out preventer can be opened.

[0041] To facilitate a better understanding of the present invention, the following examples of certain aspects of some embodiments are given. In no way should the following examples be read to limit, or define, the scope of the invention.

Examples

[0042] A subsea accumulator comprising a first chamber, a second chamber, a third chamber, a fourth chamber, and a piston system comprising a first and second piston and a connecting rod was provided. The first chamber had a piston surface area of 113 square inches. The second chamber had a piston surface area of 106 square inches. The third chamber had a piston surface area of 106 square inches. The fourth chamber had a piston surface area of 113 square inches. The diameter of the pistons were 12 inches and the diameter of the connecting rod was 3 inches.

[0043] While on the surface, where the ambient pressure was 15 psia, the first chamber, the second chamber, the third chamber, and the fourth chamber each had a pressure of 15 psia. The amount of force on each piston in each chamber was calculated and recorded. The volume of the first chamber was 1 cubic inch.

[0044] The subsea accumulator was then lowered to an operating depth were the ambient pressure was 4500 psia. The pressure in the first chamber remained at 15 psia, the pressure in the second chamber increased to 4500 psia, the pressure in the third chamber increased to 9284 psia, and the pressure in the fourth chamber increased to 4500 psia. The amount of force on each piston in each chamber was calculated and recorded. The volume of the first chamber was 1 cubic inch.

[0045] A valve on the fill line of the subsea accumulator was then opened allowing the third chamber of the subsea accumulator to be pressurized with hydraulic fluid. The pressure in the third chamber increased to 9300 psia. The pressure in the first chamber was reduced to 0.0055 psia. The amount of force on each piston in each chamber was calculated and recorded. It was noted that 11 gal of hydraulic fluid were available for use in activating a blow out preventer. The volume of the first chamber was 2714 cubic inches.

[0046] A valve on the work line of the subsea accumulator was then opened allowing the third chamber of the subsea accumulator to be depressurized. The pressure in the third chamber was reduced to 9284 psia. The pressure in the first chamber was increased to 15 psia.

[0047] Table 1 provided below illustrates the results of these tests.

Table 1

[0048] It was noted that the pressure in the third chamber remained relatively constant throughout the complete stroke of the accumulator (when the valve of the work line was opened). When pressurized with hydraulic fluid, with approximately 11.02 gallons available, the pressure in the third chamber was 9300 psia. After the valve to the work line was opened, when only approximately 0.1 gallons available of pressurized hydraulic fluid was available, the pressure in the third chamber was 9284 psia. It was also noted that by adjusting the piston diameters of the accumulator a wide range of available pressure ratios can be obtained.

[0049] While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. For example, one or more chemical and/or mechanical techniques as described herein may be used to heat the wellbore.

[0050] Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.

Claims

C L A I M S

1. A subsea accumulator comprising: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein

a first chamber is defined by the bottom surface, the outer wall, and the first piston;

a second chamber is defined by the outer wall, the interior wall, and the first piston;

a third chamber is defined by the interior wall, the outer wall, and the second piston;

a fourth chamber is defined by the outer wall, the top surface, and the second piston.

2. The subsea accumulator of claim 1, wherein the first chamber is a vacuum chamber.

3. The subsea accumulator of claim 1 or 2, wherein the second chamber is filled with sea water at ambient pressure.

4. The subsea accumulator of any one of claims 1-3, wherein the third chamber is a hydraulic chamber.

5. The subsea accumulator of any one of claims 1-4, wherein the fourth chamber is filled with sea water at ambient pressure.

6. The subsea accumulator of any one of claims 1-5, wherein the pressure in the third chamber is greater than or equal to twice the pressure in the second chamber and/or the fourth chamber.

7. The subsea accumulator of any one of claims 1-6, wherein the piston system is capable of moving up and down within the subsea accumulator.

8. The subsea accumulator of any one of claims 1-7, further comprising a fill line and a work line connected to the third chamber.

9. A blowout preventer system comprising:

a blowout preventer and

subsea accumulator, wherein the subsea accumulator comprises: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein

a third chamber is defined by the interior wall, the outer wall, and the second piston; and

10. The blowout preventer system of claim 9, wherein the first chamber is a vacuum chamber.

11. The blowout preventer system of claim 9 or 10, wherein the second chamber is filled with sea water at ambient pressure.

12. The blowout preventer system of any one of claims 9-11, wherein the third chamber is a hydraulic chamber.

13. The blowout preventer system of any one of claims 9-12, wherein the fourth chamber is filled with sea water at ambient pressure.

14. The blowout preventer system of any one of claims 9-13, wherein the pressure in the third chamber is greater than or equal to twice the pressure in the second chamber and/or the fourth chamber.

15. The blowout preventer system of any one of claims 9-14, wherein the piston system is capable of moving up and down within the subsea accumulator.

16. The blowout preventer system of any one of claims 9-15, further comprising a fill line and a work line connected to the third chamber.

17. The blowout preventer system of claim 16, where in the work line is connected to the blowout preventer.

18. A method of actuating a blowout preventer comprising:

providing a blow out preventer

providing a subsea accumulator, wherein the subsea accumulator comprises: an outer wall; an interior wall; a top surface; a bottom surface; and a piston system comprising a first piston, a second piston, and a connecting rod disposed within the subsea accumulator, wherein

a fourth chamber is defined by the outer wall, the top surface, and the second piston;

connecting the subsea accumulator to the blowout preventer via a work line, wherein the work line comprises an actuating valve; and

opening the actuating valve to actuate the blowout preventer.

19. The method of claim 18, wherein providing the subsea accumulator comprises lowering the subsea accumulator into the subsea environment.

20. The method of claim 18, wherein the subsea accumulator is pre-charged before being lowered into the subsea environment.